Pulse welding apparatus

ABSTRACT

A pulse welding apparatus using a pulse discharge such as a pulse arc welding apparatus and a short-circuit transfer arc welding apparatus. A pulse current waveform control circuit, which controls the pulse arc current so that a desired pulse arc current is supplied to the arc welding power supply for outputting the pulse arc current to the welding load unit, is constructed such that the optimum welding operation may be performed without having to adjust circuit components and modify circuit design. The pulse current waveform control circuit is in the form of a microcomputerized digital circuit which operates under a program to provide a desired pulse arc current. A modification of the program can provide any desired pulse arc currents without changing circuits. The optimum welding current waveform parameters or a target arc length signal is learned in the first welding stage and stored into a memory. An arc length feedback control or a current waveform control is performed under the control of program on the basis of the optimum welding current waveform parameters or the target arc length signal so as to control the faulty separation of globules when magnetic blow occurs and so as to reduce the variation of arc length due to external disturbances occurring at the welding torch so that improved welding quality is ensured under various environments.

TECHNICAL FIELD

The present invention relates to a pulse welding apparatus using a pulsedischarge, and more particularly to a pulse welding apparatus in whichphenomenon specific to welding such as the melting of a dischargeelectrode and separation thereof are controlled so as to obtain goodquality of welding.

PRIOR ART

Examples of conventional pulse welding apparatus using the pulsedischarge are a pulse arc welding apparatus disclosed by Japanese PatentLaid-Open No. 57-19177 and a short-circuit transfer arc weldingapparatus disclosed by Japanese Patent Publication No. 62-54585.

In the pulse arc welding apparatus, a pulse arc current is run betweenthe consuming welding wire electrode (hereinafter referred to as a wireelectrode) and workpieces, and both the workpieces and the wireelectrode are melted and then the wire electrode is cut by theelectromagnetic pinch force produced by the pulse arc discharge, and themelted electrode or globule is then transferred to the workpieces(referred to a spray transfer). A pulse welding can be carried out evenin a region where average current is less than that of a DC arc weldingapparatus, and lends itself to the welding of thinner workpieces. Thepulse welding has an advantage that the spray transfer serves toeliminate spatters produced during welding.

In the short circuit arc welding apparatus, short-circuiting isperformed alternately with arcing in a periodic fashion so that theworkpieces and the wire electrode are melted by the heat generatedthrough the arc discharge developed by an arc current between the wireelectrode and the workpieces and then the workpieces are short-circuitedto the wire electrode so as to transfer the melted globules produced onthe tip end of the wire electrode onto the workpieces. Periodicallyperforming the short-circuiting alternately with arcing assures a stablewelding operation.

In order to obtain the good quality of pulse arc welding, it is requiredthat undercut, i.e., a defective shape of welding-bead, is preventedfrom being produced and the globules that separate from the electrodeare held to substantially the same size. To prevent the spatters, thecontact between the wire electrode and the workpieces should beprevented. To prevent undercut, the arc length should be short. In orderto meet both of the requirements, it is important to ensure fineparticles of globules (spray transfer) when the globules leave theelectrode. For uniform size of globules, the uniform size of globulesthat separate from the electrode may be provided by periodicallyrepeating pulse arc currents of the same pulse shapes.

In a shield gas of a mixture of argon gas and 20% CO₂ gas, the arc sizeis large enough to enclose the globules produced on the electrode sothat the periodic simple pulses as shown in FIG. 24 (τ:pulse width,I_(B) :base current) will help the globules become particles andseparate from the electrode in a regular manner. However, in a shieldgas of 100% CO₂ gas, the arc size is rather small to enclose theglobules so that simple pulses causing phenomenon as depicted by (a) and(b) in FIG. 24, which does not ensure good welding results. Narrowerpulse widths τ provided by high position of the base current I_(B) asdepicted by (a) in FIG. 24 will change the shape of globules produced onthe tip end of electrode from Po state to Pa1 state and then to Pa2state where the globules are large enough to be separated from theelectrode. On the other hand, wider pulse widths r provided by lowposition of the base current I_(B) will cause the electromagnetic forceF due to pulse currents to be upward, which in turn causes the shape ofglobules on the tip end of wire electrode to become from Po state to Pb1state where the globules are constricted and lifted. Then, the globulesbecome as shown by Pb2 state so that the globules are separated by pulsecurrents. But the thus separated globules will spin at high speeds notto fall onto the workpieces but to be scattered as spatters to placesother than the welding point or to again be deposited on the electrodeas depicted by Pb2' state. Since the conventional pulse weldingapparatus operate as mentioned above, it suffers from the followingproblems.

When the peak level I_(P) of the pulse current is low, the globules onthe tip end of wire electrode are lifted up not allowing the separationof globules till globules grow large. Thus, the electrode isshortcircuited to the workpieces body through the globules that havegrown large. Also the spatters scatter all over the place during weldingoperation or undercut or defective beads are resulted. Furthermore, whenthe peak level Ip of the pulse current is high, there are problems tolead to a larger capacity and a more weight of the power supply unit,which causes a sharp increase in cost.

Japanese Patent Laid-Open No. Hei 1-254385 (Japanese Patent ApplicationNo. 62-309388 and No. 63-65083) discloses the inventor's pulse weldingapparatus in which a pulse current waveform is divided into a group ofpulse currents which are spaced by one or more than one pulse intervals,the groups are outputted at predetermined periods, and a continuous basecurrent is superimposed to the groups of pulse currents to provide adischarge current waveform. By this arrangement, the globulestransferred to the workpieces are converted into particles so that theglobules are transferred in a regular fashion.

As shown in FIG. 25, in the prior pulse welding apparatus JapanesePatent Laid-Open No. Hei. 1-254385, a pulse current waveform is formedof a plurality of pulse current and periodically repeated to form anentire discharge current waveform. This means that a single pulse isdivided into a plurality of pulses. The division of a pulse causes the,upward electromagnetic force on the wire electrode resulting from thepulse arc discharge to be intermittent, thereby, reducing the forcetending to lift the globule on the electrode. Therefore, the globulesare easily separated from the electrode before they grow big not only inan argon-dominated shielding gas but also in 100% CO₂ shielding gas.

The transfer of globules will be explained below. As shown in FIG. 25,when a pulse arc current having a pulse width τ and a period C_(A) isrun periodically through the wire electrode, the globules produced onthe electrode undergo "growth" and then "separation from the electrode"in a cyclic fashion. That is, a sufficient amount of globule produced onthe electrode during the early period of pulse group undergoes vibrationdue to the arc discharge at the frequency of the pulses, and separatesfrom the electrode. After the globule has separated, a new globule isproduced by pulses on the tip end of wire electrode and grows whilebeing lifted up by the electromagnetic force. Subsequently, the globulehangs from the wire tip during the base period to shape up before thenext group of pulses begins.

However, when performing arc welding while moving the wire electrodewhich produces an arc above the workpieces in a certain direction, thefollowing 2 problems should be solved before welding operation can becarried out under various conditions in wide ranges of applications.

(1) The arc is blown by the electromagnetic force generated by an arccurrent and the magnetic field due to the arc current, which is called"magnetic blow"; disturbing the regular transfer of globules.

(2) The poor quality of welding results from the variations of arclength due to external disturbances including movement of a weldingtorch in air, deformation of the workpieces, changes in wire-supplyingspeed due to the change in looseness of wire in the wire conduit, thewear of a feeding chip, and the variations in energy feeding point onthe workpieces due to the tendency of curving thereof.

Analyzing the first problem (1), when carrying out a welding operationwhile moving the wire electrode that produces an arc above theworkpieces in a certain direction, the distribution of magnetic fieldproduced in air depends on the current path, i.e., from torch to arc andthen from arc to workpieces. The shape of welding joints and differentgrounding points determine the distribution of magnetic field in air.The electromagnetic force acting on the arc depends on the distributionof magnetic field and the direction of arc current, causing magneticblow where the arc is tilted with respect to the workpieces. Thismagnetic blow results from the construction of the workpieces and thegrounding points, which appears - repeatedly if the construction of theworkpieces and the grounding points are the same.

As depicted by the respective globule separation process (A-1) to (C-1)and (A-3) to (C-3) in FIG. 26, the arc length becomes long due to thefact that the globules are lifted by the deflected arc, which disturbsthe regular separation of globules and causes the separated globules notto fall onto the beads.

As to the item (2), the variation of wiresupplying speed due to thevibration of the welding torch and the variation of looseness of wireelectrode in the wire conduit directly cause the arc length to vary;greater arc lengths result in undercut in beads and shorter arc lengthscause spatters. As shown in FIG. 27(a)-(c), the distortion of workpiecesand the external disturbances such as a decrease in feeding chip and thetendency of curving of wire electrode cause the change in heating theelectrode of a length Ex (projecting portion) between electric energyfeeding point and the tip end of wire electrode by Joule heat, which inturn causes the difference between the wiresupplying speed and thewelding speed of the tip end of wire electrode. This indirectly causesthe arc length to change. The change in arc length results in theundercuts and spatters. In other words, (1) is a steady problem thatdepends on the specific construction of workpieces and grounding points,but (2) is an unstable problem varying with each moment.

Likewise in the short-circuit arc welding apparatus, as shown in FIG. 28S1a to S3a, when a magnetic blow occurs, the arc is deflected by themagnetic blow and therefore the globules grown on the tip end of wireelectrode are lifted up to change the time length of short-circuiting ofglobules. This affects the alternate periodic transition betweenshort-circuiting and arc. Thus, beads may have unevenness on its surfaceor the depth of beads may vary, failing to ensure the welding strength.

In the conventional pulse welding apparatus, a pulse current waveformcontrol circuit controllably outputs a desired pulse arc current to anarc welding power supply unit, which supplies the welding load withpulse arc currents. The control circuit usually takes the form of ananalog circuit. Thus, if, for example, a comparing circuit is to beincorporated, there will be many adjusting elements for adjusting theamplifications of amplifiers and offset voltages as well as a largenumber of components. Additionally, for example, when changing thenumber of pulses in the pulse current group or the peak values of pulsecurrents, it is necessary to change the values of circuit components orto provide some additional circuits. This is a problem in terms of timeand cost.

SUMMARY OF THE INVENTION

The present invention was made in view of the aforementioned drawbacksand provides an inexpensive apparatus by reducing the adjusting elementsand the number of components. A first object of the invention is toprovide a pulse welding apparatus which has a pulse group currentwaveform control circuit in the form of a microcomputerized digitalcircuit by which an arbitrary current waveform is easily implementedwhenever such a current waveform is required.

A second object of the invention is to provide ashort-circuit-transfer-type pulse welding apparatus which has a pulsecurrent control circuit in the form of a microcomputerized digitalcircuit capable of preventing defective welding due to magnetic blowunder various welding conditions and environment as well as undercut andspatters caused by external disturbances to the welding torch, and whichinvolves short-circuit transfer

In order to achieve the aforementioned first object, a first inventiveaspect is to provide a pulse welding apparatus in which a current thatcauses the workpieces to melt is supplied alternately with a basecurrent or a short-circuit current to a welding load so as to performwelding operation, CHARACTERIZED by

an arc welding power supply unit for supplying pulse currents to thewelding load, in which one waveform of said pulse current is furtherdivided into a group of pulse currents which has at least one pulsewidth and at least one pulse interval, which is obtained to periodicallyrepeat said group of pulse currents and to superpose with a continuousbase current;

voltage detecting circuit for detecting the output of the arc weldingpower supply unit;

a smoothing circuit for receiving the output signal of the voltagedetecting circuit;

a voltage setting circuit for setting a desired output voltage; and

a microcomputerized digital circuit including, a digital/analogconverter circuit for outputting a voltage signal corresponding to adesired output current to the aforementioned arc welding power supplyunit,

a first analog/digital converter circuit for receiving the output signalof the voltage setting circuit,

a second analog/digital converter circuit for receiving the outputsignal of the aforementioned smoothing circuit, a data latch circuithaving a multiple bits output signal lines connected with a multiplebits input signal lines of the digital analog converter circuit,

a CPU having a data bus connected commonly to the multiple bits inputsignal lines of the data latch circuit, the multiple bits output signallines of the first analog digital converter circuit, and the multiplebits output signal lines of the second analog digital converter circuit,

wherein the CPU has an algorithm in which a digital data V_(FBA)corresponding to an average output voltage of the arc welding powersupply is compared with a digital data Vset corresponding to a desiredoutput voltage at predetermined time intervals so as to hold the basecurrent or short-circuit current, or to output a current that melts theworkpieces.

A circuit which controls the arc length so as to vary the arc length ina regular fashion, and another circuit which alternately outputs thepulse currents with the base current or a short-circuit current, areformed as the microcomputerized digital circuit. Each circuit acts undera program thereof. Therefore, the present invention provides for theelimination of the adjusting elements in the circuits to reduce thenumber of components and the adjusting time for low cost. This allowsnot only an arbitrary current waveform to be provided but also anarbitrary control operation to be implemented by modifying the programrather than changing the circuit configuration. Furthermore, since thedischarge current waveform is formed as the pulse current group, thedivision of the pulse current waveform causes the upward electromagneticforce on the wire electrode resulting from the pulse arc discharge to beintermittent, thereby reducing the force tending to lift the globule onthe electrode. Therefore, the globules are easily separated from theelectrode before they grow big without regard to the kind of shieldinggas.

In order to achieve the first object, in addition to the structuralelements of the first inventive aspect, a second inventive aspectcomprises a third analog digital converter circuit that has a multiplebits output signal lines connected to the data bus which is connected tothe data bus, and receives the output of the voltage detecting circuit.And while the arc welding power supply unit outputs the base- current orshort-circuit current, the CPU performs operations according to theaforementioned algorithm at predetermined intervals, as well as comparesa digital data V_(FBM) corresponding to a momentary output voltage ofthe arc welding power unit with a digital data Vmax in which thecharacter is Vmax>Vset corresponding to the predetermined digital dataVset. The CPU holds the base current or short-circuit current if V_(FBM)<Vmax, and the CPU output a second base current greater than the basecurrent or short-circuit current only when V_(FBM) ≧Vmax. The secondinventive aspect makes it possible to implement a circuit, whichprevents magnetic blow while the base current or short-circuit currentis flowing during pulse arc welding operation, by arranging theoperation such that when the output voltage exceeds the setting Vmaxduring the supply of base current (or short-circuit current), the secondbase current or short-circuit current is run: In addition to the effectsof the first inventive aspect, this is advantageous in that a commonlyknown magnetic-blowpreventing circuit can easily be provided

In order to achieve the second object, a third to tenth inventiveaspects were made.

The third inventive aspect comprises:

an arc length detector for detecting a signal indicative of the arclength between the wire tip end and the workpieces;

a microcomputerized digital circuit including a target arc length memoryfor storing therein a target arc length signal indicative of the pulsecurrent group, an arc current waveform memory for storing arc currentwaveform parameters including respective peak values of the pulsecurrent group, base current, pulse widths, and pulse interval, and acalculating unit for correcting the current waveform parameters on thebasis of difference between the detected-arc-length signal and thetarget-arc-length signal to output an arc current signal whose waveformof pulse current group is controlled; wherein the calculating unithaving an algorithm which includes storing means for storing into thearc current waveform memory the arc current waveform parameters whosewaveforms are controlled in accordance with a welding area in a firstwelding stage, and control means for reading out, in a second weldingstage, the thus stored arc current waveform parameters corresponding tothe respective welding areas and for controllably increasing ordecreasing the thus read current waveform parameters on the basis of thedifference between the detected-arc-length signal and thetarget-arc-length signal.

Thus, in addition to the effects of the first and second inventiveaspects, the third inventive aspect eliminates the-variation of arclengths due to magnetic blow in the first welding stage so as to reducethe faulty of separation of the globules caused by the magnetic blow.This provides "learned" waveform parameters of welding current which areadjusted to actual effects of magnetic blow occurring in the respectivewelding regions. Feedback-controlling the arc length with reference tothe welding current waveform learned in the first welding stage, reducesthe faulty separation of globules due to magnetic blow as well as thevariations of arc length in the welding torch due to externaldisturbances, thereby improving welding quality under various weldingconditions.

A fourth inventive aspect comprises, in addition to the structuralelements of the third inventive aspect, a short-circuit detector fordetecting short-circuiting and a short-circuit current waveform memoryfor storing a short-circuit current to be supplied when short-circuitoccurs. The calculating unit has the algorithm in which theshort-circuit current is read out from the short-circuit currentwaveform memory and is supplied to the welding load. A predeterminedcurrent waveform is split into a short-circuit current waveform and anarc current waveform. When a sudden short-circuiting occurs due toexternal disturbances during the regular welding, the current waveformis immediately switched to the short-circuit waveform. Thus, in additionto the effects derived from the third inventive aspect, the fourthinventive aspect is effective in performing high quality weldingoperation.

A fifth inventive aspect is of the same construction as the fourthinventive aspect. The calculating unit has the algorithm in which uponthe detection signal from the short-circuit detector, the short-circuitcurrent is read out from the short-circuit current waveform memory andthe short-circuit current waveform is supplied to the welding load, andwhen the short-circuit removal signal is issued from the short-circuitdetector, the arc current waveform is reset and then the arc currentwaveform is supplied to the welding load. When the short-circuit occurs,the short-circuit current is run immediately and after the short-circuitis removed the arc current waveform is once reset before supplying thearc current waveform to the welding load. Thus, the same effects as inthe third inventive aspect are obtained in the short-circuit transferarc welding.

A sixth inventive aspect has, in addition to the construction in thethird and fourth inventive aspects, a separation detector for detectingthe separation of the globules produced on the tip end of wireelectrode. The calculating unit has an algorithm in which during theregular welding as the second welding stage, the amount of charge ofcurrent after separation is detected on the basis of the waveformbarometer of the welding current "learned" in the first welding stage inresponse to the detection signal from the separation detector so that aminimum base current is supplied when the amount of charge exceeds apredetermined value. In addition to the effects derived from the thirdand fourth inventive aspects, the sixth inventive aspect has advantagesin which a uniform separation amount of globule may be achieved forperforming welding operation in a regular manner by detecting the amountof charge of current at a time when the separation has begun and bydecreasing the current when the detected charge amount reaches apredetermined value.

In addition to the construction in the third inventive aspect, a seventhinventive aspect has an algorithm which includes a storage means forstoring into the target arc length memory the target arc length signalcorrected in accordance with the detected arc length signal when weldingis performed through the use a current waveform according to the arccurrent waveform parameters which are preset in the first welding stage,and a control means which reads out the "learned" target arc lengthsignal and the arc current waveform parameters stored in the secondwelding, and then increases or decreases the arc current parameters inaccordance with the difference between the detected arc length signaland the learned target arc length signal. Thus, in addition to theeffects derived from the first and second inventive aspects, the seventhinventive aspect is advantageous in that in the first welding stage theseventh inventive aspect eliminates the effects of the variation of arclength due to magnetic blow to reduce faulty separation of globule. Theseventh inventive aspect makes it possible to obtain the learned targetarc length signal which has taken the magnetic blow in the respectivewelding area into account. Controlling the current waveform withreference to the target arc length learned in the first welding stage,can reduce not only the faulty separation of globule due to magneticblow but also the variation of arc length due to external disturbancesoccurring at the welding torch. Thus, the improvement in welding qualitymay be assured under various welding conditions.

In addition to the construction of the seventh inventive aspect, aneighth inventive aspect has a short-circuit detector for detectingshort-circuit. The calculating unit has an algorithm in which theshort-circuit current stored in the short-circuit current waveformmemory is read out in response to the detection signal from theshort-circuit detector, and then the short-circuit current waveform issupplied. A predetermined current waveform is split into theshort-circuit current waveform and the arc current waveform. This allowsto immediately switch to the short-circuit current waveform when asudden short-circuiting occurs due to external disturbances whenperforming regular welding. Thus, in addition to the effects derivedfrom the seventh inventive aspect, the eighth inventive aspect iscapable of performing good welding operation with improved quality ofproducts.

The ninth inventive aspect has the same structural elements as in theeighth inventive aspect. The calculating unit includes an algorithm inwhich the short-circuit current stored in the short-circuit currentwaveform memory is read out in response to the detection signal from theshort-circuit detector and is supplied, and the arc current waveform isreset before resuming the supply of arc current waveform when theshort-circuit removal signal is issued from the short-circuit detectorWhen a short-circuit occurs, the short-circuit current is immediatelysupplied and after the short-circuit is removed the arc current waveformis reset to supply the arc current waveform. Thus, the eighth inventiveaspect provides the same effects as in the seventh inventive aspect inshort-circuit transfer arc welding.

In addition to the construction of the seventh and eighth inventiveaspects, a tenth inventive aspect has a separation detector fordetecting the separation of globules produced on the tip end of wireelectrode. The calculating unit has an algorithm in which whenperforming the second welding stage, the charge amount of current afterseparation is detected in response to the detection signal on the basisof the waveform barometer of welding current learned in the firstwelding so as to supply a minimum base current when the charge amountexceeds a predetermined value. Thus, in addition to the effects derivedfrom the seventh and eighth inventive aspect, the amount of globuleswhen separating may be made substantially constant by detecting theamount of charge of current based on a time when separation occurs anddecreasing the current when the detected amount of charge reaches apredetermined value. Thus, welding may be carried out in a regularfashion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an embodiment of a pulse weldingapparatus according to a first inventive aspect;

FIGS. 2(a) and 2(b) are illustrative diagrams illustrating the waveformof an output current of the arc welding power supply unit in FIG. 1,supplied to an arc load;

FIGS. 3(a) and (b) are flowcharts of a program under which a CPUperforms a control operation for the apparatus in FIG. 1;

FIGS. 4, 5, and 6 are block diagrams showing other embodiments of apulse welding apparatus according to the first inventive aspect;

FIG. 7 is a block diagram showing an embodiment of a pulse weldingapparatus according to a second inventive aspect;

FIGS. 8(a) and 8(b) are flowcharts of a program under which a CPUperforms the control operation of the apparatus in FIG. 7;

FIG. 9 shows an overall construction of the pulse welding apparatusexplaining a third to tenth inventive aspects;

FIG. 10 shows the construction of an arc length detector (81) in FIG. 9;

FIGS. 11(a) and 11(b) are illustrative diagrams illustrating theconstruction of the arc current waveform memory (85) and the target arclength memory (86);

FIG. 12 is an illustrative diagram of the pulse current waveform;

FIGS. 13(a) and (b) illustrates the first welding stage and the secondwelding stage according to the third inventive aspect;

FIGS. 14A, 14B and 15A, 15B are flowcharts of the operation of acalculating unit (88) when the first and second welding stages of thethird inventive aspect are performed;

FIG. 16 is a flowchart of the calculating unit (88) according to afourth inventive aspect;

FIG. 17 is a flowchart of the calculating unit (88) according to a fifthinventive aspect;

FIG. 18 is a flowchart of the calculating unit (88) according to a sixthinventive aspect;

FIG. 19 and FIG. 20 are flowcharts of the calculating unit (88) when thefirst and second welding stages according to the seventh inventiveaspect are performed;

FIG. 21 is a flowchart of the calculating unit (88) according to aneighth inventive aspect;

FIG. 22 is a flowchart of the calculating unit (88) according to a ninthinventive aspect;

FIG. 23 is a flowchart of the calculating unit (88) according to a tenthinventive aspect;

FIGS. 24(a) and 24(b) are illustrative diagrams of a prior art pulse arcdischarge current waveform and the transfer of globules;

FIG. 25 shows the operation and effects of a prior art pulse currentgroup;

FIG. 26 is an illustrative diagram of magnetic blow;

FIGS. 27(a), 27(b) and 27(c) are illustrative diagrams of the variationof the welding conditions; and

FIG. 28 is a diagram showing the current waveform and the transfer ofglobule in a prior art short-circuit arc welding method.

BEST MODE OF EMBODIMENT OF THE INVENTION

FIG. 1 shows a construction of an embodiment of a pulse weldingapparatus according to a first inventive aspect. In the figure,reference numeral 10 is an arc welding power supply unit that includesan inverter circuit, high frequency transformer, and high frequencydiodes, all being controllably driven by an inverter drive circuit.Reference numeral 5 denotes an arc load which includes a welding torch51, a wire electrode 52 to which wire electrode is supplied in the formof wire from the wire reel, an arc discharge 53, and workpieces 54.Inverter-controlled desired pulse groups are supplied through the highfrequency transformer and high frequency diodes from the invertercircuit having the arc welding power supply 10 to the welding torch 51for arc welding operation.

Reference numeral 11 is a consuming electrode (hereafter referred to asa wire) and reference numeral 12 is a wire supplying roller forsupplying the wire 11. Reference numeral 13 is a wire supplying motormechanically connected to the wire supplying roller 12 through gears.Reference numeral 14 is a motor drive circuit connected to a wiresupplying motor 13, and reference numeral 15 is a motor speed settingcircuit connected to the motor drive circuit. Reference 7 is a voltagedetecting circuit connected to an output terminal of the arc weldingpower supply 10 and reference numeral 16 is a smoothing circuit thatreceives the output of the voltage detecting circuit 7. Reference 17shows a voltage setting circuit. The pulse current waveform controlcircuit 8 receives the detected value from the voltage detecting circuit7 via the smoothing circuit 16 and the setting value of the voltagesetting circuit 17 so as to control the waveform of pulse current groupsoutputted from the arc welding power supply 10.

The aforesaid pulse current waveform control circuit 8 is provided witha D/A converting circuit 18 for outputting a voltage signalcorresponding to a desired output current to the arc welding powersupply unit 10, a first A/D converting circuit 19 that receives theoutput signal of the voltage setting circuit 17, a second A/D convertingcircuit 20 that receives the output signal of the smoothing circuit 16,a data latch circuit 21 connected to a plurality of data input line ofthe D/A converting circuit, a CPU 22, a ROM 23, and an address decodercircuit 24. The control circuit 8 is a microcomputerized digitalcircuit. Reference numeral 25 is an address bus for the CPU, referencenumeral 26 is a data bus for the CPU, reference numeral 27 is a readsignal outputted from the CPU, and reference numeral 28 is a writesignal outputted from the CPU. Reference numerals 29-32 are a data latchcircuit selection signal, a first A/D converting circuit selectionsignal, a second A/D converting circuit selection signal, and a ROMselection signal, respectively. The CPU 22 is connected via a commondata bus 26 with multibit input signal lines of the data latch circuit21, multibit input signal lines of the first A/D converting circuit 19,and multibit input signal lines of the second A/D converting circuit 20.The CPU 22 operates according to an algorithm, when the arc weldingpower supply unit 10 outputs the base current or the short-circuitcurrent, in which a digital data V_(FBA) indicative of an average outputvoltage of the arc welding power supply unit is compared with a digitaldata Vset indicative of a desired output voltage at predetermined timeintervals so as to output a base current or a short-circuit current, ora current for melting the workpieces instead of a base current orshort-circuit current.

The operation of the present invention will now be described. In FIG. 1,the arc welding power supply unit 10 outputs to the arc 53 the pulsegroup current alternately with the base current or short-circuit currentso as to perform pulse arc welding. FIGS. 2(a) and 2(b) are illustrativediagrams illustrating the waveform of the output current, (1)representing the period for pulse group current, (2) indicating theperiod during which the base current or short-circuit current isoutputted.

ROM 23 contains a program for controlling the operation in which avoltage signal indicative of a desired output current is outputted, andin which the average output voltage of the arc welding power supply 10is controllably held.

FIGS. 3(aand 3(b) are flowcharts showing the steps of the programexecuted by the CPU. In the figures, (a) shows the control when the basecurrent is outputted and (b) shows the control when short-circuitcurrent is outputted. These controls are performed at predetermined timeintervals as an interrupt program of the main program shown.

A voltage signal indicative of the average output voltage of the arcwelding power supply unit 10, which is outputted via the voltagedetecting circuit 7 and the smoothing circuit 16 while the current orshort-circuit current is being supplied (Sa1, Sb1), is converted into adigital data by the second A/D converting circuit 20 at predeterminedtime spaces under the control of the program stored in the ROM 23. Theselection signal 31 is obtained through the address decoding circuit 24which decodes the address data and the read signal 27 of the CPU 22outputted onto the address data and the read signal 27 of the CPU 22outputted onto the address bus 25. The selection signal serves as astart signal of the second A/D converting circuit 20 as well as asampling signal (Sa2, Sb2) for a sample-and-hold circuit incorporated inthe second A/D converting circuit 20.

The thus obtained digital data V_(FBA) indicative of the average outputvoltage is inputted into the CPU 22 via the data bus 26 (Sa3, Sb3) to becompared with the digital data Vset prestored in the CPU 22 (Sa4, Sb4).

When supplying the welding load 5 with a waveform shown in FIG. 2(a), adigital data I_(base) indicative of the base current is outputted to thedata latch circuit 21 if V_(FBA) ≦ Vset (Sa5), and a data indicative ofthe pulse current group is outputted to the data latch circuit 21 ifV_(FBA) <Vset (Sa6, Sa7).

When supplying the welding load unit with the waveform shown in FIG.2(b), the digital data I_(base) indicative of the short-circuit currentis outputted to the data latch circuit 21 if V_(FBA) ≦Vset (Sb5), and adata indicative of the pulse current group is outputted to the datalatch circuit 21 if V_(FBA) >Vset (Sb6, Sb7).

In FIGS. 3(a) and 3(b), the digital data Vset is set within the mainprogram and indicates the output signal of the voltage setting circuit17 in FIG. 1. The output signal of the voltage setting circuit 17 isconverted into a digital data by the first A/D converting circuit 19 andis inputted into the CPU 22 via the data bus 26 so that the digital datais stored into a register therewithin. The above-mentioned signalprocessing is carried out under the main program.

In FIG. 1, the data latch circuit selecting signal 29 is outputted fromthe address decoding circuit 24 in combination with the address data andwrite signal 28 outputted onto the address bus 25. The signal 29 servesas a clock pulse for a plurality of flip flops that form a data latch 21so as to latch the data indicative of the base current or pulse groupcurrent outputted onto the data bus 26 of the CPU 22. The data held onthe plurality of output signal lines of the data latch circuit 21 isconverted by the D/A converter 18 into an analog voltage which isoutputted to the arc welding power supply unit 10, which in turnprovides a desired output current.

In FIG. 1, the first A/D converting circuit selection signal 30 isobtained by decoding the address data outputted onto address bus 25 andthe read signal 27 outputted from the CPU 22 by the address decoder 24.The first A/D converting circuit selection signal 30 serves as asampling signal for the sample-and-hold circuit in the first A/Dconverting circuit 19 and a start signal for the first A/D convertingcircuit 19. The ROM selecting signal 32 is a signal obtained by decodingthe address data outputted onto the address bus 25 and the read signal27 by the address decoder circuit 24, and functions as a CE signal forthe ROM 23.

FIG. 4 is a block diagram showing another embodiment of the firstinventive aspect. In FIG. 4, the CPU 22 is constructed of a single-chipCPU incorporating at least more than one A/D converting circuits.Reference numeral 33 is a first analog input port and reference numeral34 is a second analog input port. The apparatus of the construction inFIG. 4 will also perform an operation similar to the embodiment in FIG.1 under the program shown in FIG. 3.

FIG. 5 is a block diagram showing still another embodiment of theinvention. In the figure, the CPU 22 is constructed of a single-chip CPUhaving a ROM therein into which the program shown in FIG. 3 is stored.This embodiment is also adapted to operate in a manner similar to theembodiment in FIG. 1.

FIG. 6 is a block diagram showing yet another embodiment of the firstinventive aspect. In the figure, the CPU 22 is constructed of asingle-chip CPU having at least more than one A/D converting circuit anda ROM therein. The apparatus shown in FIG. 6 is also adapted to operatein a manner similar to that shown in FIG. 1.

According to the first inventive aspect, since the discharge currentwaveform is formed as the pulse current group, the division of the pulsecurrent waveform causes the upward electromagnetic force on the wireelectrode resulting from the pulse arc discharge to be intermittent,thereby reducing the force tending to lift the globule on the electrode.Therefore, the globules are easily separated from the electrode beforethey grow big without regard to the kind of shielding gas. The growingof the globule formed on the wire electrode alternates the separation ofthe globule like clockwork. A microcomputer is used as a circuit whichcontrols the welding load unit so that the regular variation of arclength is ensured and a circuit which outputs the pulse group currentsalternately with the base current or the short-circuit current. Thus,the circuits are implemented by control operations under a program andare advantageous in that:

(1) No adjustment of circuit elements is required so that the number ofparts and adjusting time can be saved for low apparatus cost.

(2) A desired output current waveform can be provided at will bymodifying the program, i.e., the replacement of a ROM, without changingthe circuits, and the control operation can be changed at will withoutchanging the circuits.

FIG. 7 represents an embodiment of a second inventive aspect. The sameelements as those in FIG. 1 have been given the same reference numeralsand the detailed description thereof is omitted. In FIG. 7, thereference numeral 35 is a third A/D converting circuit which receivesthe output signal of the voltage detector 7, and reference numeral 36 isa third A/D converting circuit selection signal outputted from theaddress decoder 24. The construction in FIG. 7 includes a third A/Dconversion circuit 35 which has a plurality of output signal linesconnected to the data bus 26 and which receives the output signal of thevoltage detecting circuit 7. The construction in FIG. 7 operatesaccording to the algorithm in FIG. 3 at predetermined time intervalswhile the arc welding power supply unit 10 outputs the base current orshort-circuit current. The construction in FIG. 7 also has the algorithmin which the digital data V_(FBM) indicative of an instantaneous outputvoltage of the arc welding power supply current is compared with thedigital data Vmax, where Vmax>Vset and Vset is the desired digital data,and the base current or short-circuit current is maintained if V_(FBM)<Vmax, and a second base current or short circuit current greater thanthe base current or short current only when V_(FBM) ≧Vmax.

The operation of the CPU 22 will now be described with reference toFIGS. 8(a) and 8(b) similar to FIGS. 3(a) and 3(b). In FIG. 7, while thearc welding power supply unit 10 supplies the base current (Sa1, Sb1),the voltage signal indicative of the instantaneous output voltage of thearc welding power supply unit 10 is outputted from the voltage detector7, and the voltage signal is converted by the third A/D convertingcircuit 35 into a digital data under the control of the program shown inFIG. 8 (Sa2-Sa5, Sb2-Sb5). As shown in FIG. 8, the digital data V_(FBM)is compared with the data Vmax prestored in the main program (Sa6-Sa7,Sb6-Sb7) so as to output a data indicative of the base current orshort-circuit current to the data latch circuit 21 when V_(FBM) <Vmax(Sa8, Sb8), and to output a second base current or short-circuit currentgreater than the base current to the data latch circuit 21 when V_(FBM)≧Vmax (Sa9, Sb9). Additionally, when V_(FBM) <Vset, the program proceedsto supplying the pulse current group (Sa10, Sa11, Sb10, Sb11). In FIG.7, the third A/D converting circuit selection signal 36 is obtainedthrough the address decoder circuit 24 which decodes the address dataoutputted from the address bus 25 and the read signal 27 of the CPU, andfunctions as a start signal of a sampling signal of the sample-and-holdcircuit included in the third A/D converting circuit 35.

With the construction in FIG. 7 and under the program in FIG. 8, whenthe output voltage exceeds the setting value Vmax while the base current(or short-circuit current) is supplied, the apparatus supplies thesecond base current or short-circuit current so as to act as a circuitin which the magnetic blow or so-called Arc-blow is prevented while thebase current or short-circuit current is flowing in pulse arc welding.

In other words, according to the embodiment of the second inventiveaspect, a magnetic-blow preventing circuit can easily be implementedwhile also exhibiting the effects derived from the first inventiveaspect.

In FIG. 7, the CPU 22 may be of a single-chip type which incorporatesthe first to third A/D converting circuits 19, 20, and 35, and the ROM23. While the embodiments of the aforementioned respective inventiveaspects have been described with respect to the group current (pulsegroup) having one or more than one pulselike peak current and basecurrent, any other current waveforms may be used if they are of thewaveform which causes the workpieces as an electrode to melt.

The voltage detecting circuit, which detects the voltage of the weldingload circuit in accordance with the conditions of welding load such asthe output voltages of the arc welding supply unit and arc lengths, maybe of a voltage detecting circuit that detects the signal voltageindicative of the welding conditions such as arc length instead of theoutput voltage of the arc welding power supply unit.

A specific example will be described of a pulse welding apparatus inwhich a current waveform control circuit is provided in the form amicrocomputerized digital circuit so as to prevent poor welding resultsdue to magnetic blow, undercuts, or spatters attended with the externaldisturbances to the welding torch under various welding conditions andenvironment.

FIG. 9 shows an overall construction of a pulse welding apparatus forexplaining the respective embodiments of the third to tenth inventiveaspects. In the figure, reference numeral 1 is an inverter circuit whichis controllably driven by the inverter drive circuit 2, referencenumeral 3 is a high frequency transformer, reference numerals 4A and 4Bare high frequency diodes, all forming the arc welding power supply 10.Reference numeral 5 is an arc load unit which is constructed of awelding torch 51, wire electrode 52 supplied through the torch 51accommodated in a wire reel, arc discharge 53, and workpieces 54. Adesired pulse group current waveform i, inverter-controlled, is suppliedfrom the aforementioned inverter circuit 1 to the welding torch 51 viathe transformer 3 and the high frequency diodes 4A and 4B so as toperform arc welding.

Reference numeral 6 is a current detector for detecting theaforementioned pulse group current, and reference numeral 7 is a voltagedetector for detecting the voltage across the electrodes; referencenumeral 8 is a pulse current waveform control circuit which drives theaforementioned inverter circuit i to control the waveform of the outputpulse current on the basis of the current detected by the currentdetector 6 that detects the aforementioned pulse current i and thevoltage detected by the aforementioned voltage detecting circuit 7. Thepulse current waveform control circuit 8 is provided with an arc lengthdetector 81 for detecting the signal L(l) indicative of arc lengthbetween the tip of wire electrode and the workpieces on the basis of thevalues I and V detected by the aforementioned current detector 6 and thevoltage detector 7, a short-circuit detector 82 for outputting ashort-circuit detection signal when the detected signal L(l) of the arclength detector 81 does not reach a predetermined level, a separationdetector 83 for detecting the separation, and a microcomputerizeddigital circuit 100. Furthermore, the microcomputerized digital circuit100 includes an A/D converter 84 for converting the analog signaldetected by the arc length detector 81 into digital, an arc currentwaveform memory 85 in which the pulse peak current value Ip(n), basecurrent value I_(B) (n), pulse width τ(n), and pulse intervals C_(A) (n)of the respective pulses, all for constituting the pulse current groupwhich is supplied via the external input/output port (9), are stored, atarget arc length memory 86 where the target arc length Lo(n) is stored,a short-circuit current waveform memory 87 where the short-circuitcurrent Is(n) supplied when short-circuiting, and a calculating unit 88in the form of a CPU which produces and supplies a comparator 89 with apulse current lo whose waveform has been shaped so that the adverseeffects from external disturbances during welding operation and weldingarea on the basis of the values stored in the respective memories andthe detector outputs of the respective detectors. The aforementionedcomparator 89 compares the pulse current Io with the detected value ofcurrent i so as to output a control signal in accordance with thecomparison result to the inverter control circuit 2.

The aforementioned arc length detector 81 comprises buffer amplifiers81a and 81b, a multiplier 81cwhich reads the detected current i via thebuffer amplifier 81a and produces a positive characteristic constantK1(i)i of the arc voltage as a result of multiplying K1(i) by thecurrent i, an offset voltage constant setting unit 81d for setting theoffset voltage constant K2, an adder 81e which adds the outputs of theaforementioned multiplier 81c and the DC voltage constant setting unit81d, and a comparator 81f which produces a comparison output L(l)=V-Vxin accordance with the arc length by comparing the added outputVx=K1(i)i+K2 of the adder 81e with the detected voltage V from thevoltage detector 7. The arc length detector 81 detects the arc voltagein accordance with the arc length on the basis of the detected voltageand detected current.

The arc voltage V may be expressed by V=R(i)i+Al+B where R(i) is thepositive characteristic constant of arc, i is an arc current, A is aproportional constant for an arc length, l is the arc length, and B is aminimum voltage. From a point of view of circuit design, the voltage isexpressed by Vx=K1(i)i+K2 where K1(i) is the positive characteristicconstant and K2 is the offset voltage constant. Therefore, thedifference (Ll)=V-Vx turns out to be L(l)=V-Vx={R(i)-K1(i)}i+Al+B-K2. IfR(i) and K1(i) are selected so that R(i) is nearly equal to K1(i), then(Ll) is nearly equal to Al+(B-K2), being reduced to a function of onlythe arc length. Thus, selecting proper values of A, B, and K2, thedifference L(l)=V-Vx outputed from the comparator 85f becomes the arclength signal indicative of an actual arc length.

The arc current waveform memory 85 has, as shown in FIGS. 11(a) and11(b), a first memory area (FIG. 11(a)) for storing the respective pulsepeak values Ip(n), base currents I_(B) (n), pulse widths τ(n) and pulseintervals C_(A) for n=1 to n_(o) of pulse group as shown in FIG. 12supplied from the external input/output port 9, and a second memory area(FIG. 11(b)) where the respective pulse peak values Ip(m,n), basecurrent values I_(B) (m,n), pulse widths τ(m,n), and pulse intervalsC_(A) (m,n) of the pulse current group produced on the basis of laterdescribed "learning" welding for each of respective regions m=1 to m_(o)obtained by dividing the workpieces from the center thereof by specificangles when welding the peripheral portion of the workpieces 54 at aspecific speed.

A specific embodiment of a third inventive aspect will now be described.The third inventive aspect is a pulse welding apparatus having aconstruction shown in FIG. 9 with the short-circuit detector 82,separation detector 83, and short-circuit current waveform memory 87eliminated. The calculating unit 88 has the algorithm formed of astorage means where in the first welding stage, the arc current waveformparameters stored in the first memory area (FIG. 11(a)) in the arccurrent waveform memory 85 defined through the external input/outputport 9 are corrected for the respective welding regions in accordancewith the difference between the detected arc length signal and thetarget arc length signal, and is then stored into the secondary memoryarea (FIG. 11(b)) of the aforementioned arc current waveform memory 85,and a control means by which the aforementioned arc current waveformparameters stored are read out after the second welding stage for therespective welding and are increased or decreased in accordance with thedifference between the detected arc length signal and the target arclength signal.

The operation of the third inventive aspect will be described referringto the flowcharts for the calculating unit 88 shown in FIGS. 14 and 15with respect to a case where the workpieces 54 in FIG. 13(a) are weldedat its periphery.

FIG. 14 shows a flowchart of the first welding stage of the presentinvention as a "learning welding". Welding is performed in accordancewith the pulse current waveform parameters stored in the first memoryarea shown in FIG. 11(a) of the arc current waveform memory 85 definedthrough the external input/output pot 9. During which the aforementionedarc current waveform parameters for the respective welding apparatus arecorrected in accordance with the difference between the detected arclength signal and target arc length signal. The arc current waveformparameters controllably adjusted its waveform for the welding region arestored into the second memory area of the aforementioned arc currentwaveform memory 85 in FIG. 11(b) FIG. 15 shows a flowchart of the secondwelding stage of the present invention in which the arc current waveformparameters stored in the second memory area in the aforementioned firstwelding stage are read out for the respective welding regions and arethen increased or decreased in accordance with the difference betweenthe detected arc length signal and the target arc length signal.

In the first welding as a learning welding in FIG. 14, the respectiveparameters Ip(n), I_(B) (n), τ(n), C_(A) (n) and target arc length lo(n)of the pulse current group are inputted through the externalinput/output port 9 into the first memory areas of the arc currentwaveform memory 85 and the target arc length memory 85.

With this condition, as shown in FIG. 13(a), the calculating unit 88reads (step S5) the arc current waveform parameters Ip(n), I_(B) (n),τ(1), C_(A) (1), and Lo(1) from the arc current waveform memory 85 andthe target arc length memory 86 for m=1 and n=1 (steps S1-S4) where m isthe iterative loop for a welding region information and n is theiterative loop of the respective pulse current group outputted to therespective welding region. Then the welding current in accordance withthese parameters is outputted to the comparator 89 (steps S6 and S7).

In this manner, the pulse current lo is outputted from the calculatingunit 88 to the comparator 89 which in turn outputs an ON signal to theinverter drive circuit 2 so that the inverter drive signal istransmitted from the inverter drive circuit 2 to the inverter circuit 1to drive the inverter. Driving the inverter causes the shapedalternating waveform to be outputted to the high frequency transformer 3whose output is rectified by the high frequency diodes 4A and 4B into aDC waveform so as to supply the arc load unit 5 with the pulse arccurrent waveform i. The pulse waveform i produces the pulse arcdischarge 53 across the wire electrode 52 and the workpieces 54 so thatthe workpieces and the tip end of wire electrode 52 are melted by thepulse discharge 53.

At this time, the arc length detector 81 detects the arc length L(l) onthe basis of the detection signal I and V from the current detector 6and the voltage detector 7, respectively, and outputs the arc lengthL(l) to the calculating unit 88. The calculating unit 88 reads out boththe aforementioned detected arc length L(l) and the target arc lengthLo(l) in the target arc length memory 86 (steps S9) when the arc currentsupply is completed for n=1 i.e., when T=τ(1)+C_(A) (1) (step S8). Then,the difference ΔL=L(l)-Lo(1) is calculated (step S10) and the arccurrent waveform parameters are corrected by the following equations(step S11).

    Ip(m,n)=Ip(n)-B.sub.1 ΔL

    I.sub.B (m,n)=I.sub.B (n)-B.sub.2 ΔL

    τ(m,n)=τ(n)-B.sub.3 ΔL

    C.sub.4 (m,n)=C.sub.A (n)-B.sub.4 ΔL

B1-B4 are proportional constants.

Parameters to be stored into the second memory area are obtained by thefollowing equations on the basis of the above-corrected arc currentparameters and the arc current parameters stored in the first memoryarea of the arc current waveform memory 85 (step S12).

    Ip(m,n)=1/2[Ip(m,n)+Ip(n)]

    I.sub.B (m,n)=1/2[I.sub.8 (m,n)+I.sub.B (n)]

    τ(m,n)=1/2[τ(m,n)+τ(n)]

    C.sub.A (m,n)=1/2[C.sub.A (m,n)+C.sub.A (n)]

Then, after going through steps S14-S16, the time t is cleared to t=0and then the program returns to step S4 where the iterative loop n isupdated to n=2. If n≧2, then the arc current waveform parameters and thetarget arc length detection signal are read in at step S5 so as tocorrect the arc current waveform parameters by the similar equations tostep S12 on the basis of the difference ΔL between the arc lengthdetection signal L(l) and the target arc length Lo(n) (step S17 andS18). The arc length detection signal L(l) when the difference signal ΔLis determined is the value when sampling was last made last for n-1.Pulses are outputted on the basis of the above-corrected arc currentwaveform parameters (step S19 and S20).

Then, the arc length detection signal L(l) based on the pulse output areread (step S21) and the program returns to step S12 where the parametersto be stored into the second memory area are obtained on the basis theabove-corrected arc current waveform parameters and the arc currentwaveform parameters stored in the first memory area of the arc currentwaveform memory 85.

This process is carried out consecutively for the respective pulsecurrent groups till n=n_(o) and for the total output time till T=Tc(step S15, S22).

In steps S16 or S22, the program proceeds to the next welding regionwhen T=Tc. Thus, the program returns to step 2 where the iterative loopof welding region is updated. The above-mentioned operation is repeatedto correct the parameters for the respective welding regions along theshape of the workpieces 54 shown in FIG. 13(a), and the correctedparameters are stored into the second memory area shown in FIG. 11(b).In step S14, when T=To, the time is cleared to T=0 (step S23) tocomplete learning welding. FIG. 13(b) shows the output waveforms of therespective pulse groups at this time.

Therefore, as mentioned above, the respective parameters stored in thesecond memory area of the arc current waveform memory 85 in the firstwelding stage, are used to eliminate the effects of variation of the arclength due to magnetic blow so that the faulty separation of globulesdue to magnetic blow is controlled. The parameters are then stored aswaveform parameters which are learned taking into account the magneticblow in the respective welding regions.

Furthermore the learning welding as the first welding stage is followedby the regular welding as the second welding stage shown in FIG. 15. Theregular welding shown in FIG. 15 is basically the same as the flow oflearned welding in FIG. 14 except that at step S28 similar to step S5 inFIG. 14, the arc current waveform parameters Ip(m,n), Ip(m,n), τ(m,n),C_(A) (m,n) in the second memory area of the arc current waveform memory85, which are learned in the learning welding and are shown in FIG.11(b), are read in; steps S11 and S12 are omitted; at step S39 similarto step S18, the arc current waveform parameters stored in the secondmemory area is corrected on the basis of the difference ΔL between theprevious arc length detection signal L(l) of the iterative loop and thetarget arc length signal Lo(n) the pulses are outputted based on thethus corrected parameters.

Thus, in the regular welding as the second welding, the arc length isfeed-back controlled with reference to the welding current waveformparameters learned in the first welding stage, so that the faultyseparation of globules due to the magnetic blow is controlled as well asthe arc length variation occurring at the welding torch due to externaldisturbances is controlled, improving the quality of welding undervarious welding environments.

Hence, in addition to the effects derived from the embodiments of thefirst and second inventive aspects, the third inventive aspect has theadvantages that the variation of arc length due to the magnetic blow iseliminated in the first welding stage so as to reduce the faultyseparation of globules resulted from magnetic blow, the learned waveformparameters are obtained taking the magnetic blow into account in therespective welding regions, and the feedback control of arc lengthfeedback with reference to the welding current waveform parameterslearned in the first welding stage reduces not only the faultyseparation of globules due to magnetic blow but also the variation ofarc length due to external disturbances occurring at the welding torch.Therefore, the welding quality is ensured under various weldingenvironments.

A specific example of the fourth inventive aspect will now be described.The fourth inventive aspect is a pulse welding apparatus of the overallconstruction in FIG. 9 with the separation detector 83 eliminated. Thecalculating unit 88 has the algorithm in which when the short-circuit isdetected by the short-circuit detector 82 in the second welding stage,the short-circuit current is read out from the short-circuit currentwaveform memory 87 where both the step-wise short-circuit current Is(S)supplied when short-circuiting and the supplying period τs(S), arestored.

That is, the short-circuit current waveform memory 87 holds both thesupply period τs(S) (S=1, 2, . . . , So) and the stair-case-likeshort-circuit current Is(S) whose magnitude is controlled via theexternal input/output port 9 to increase in steps. The calculating unit88 performs short-circuit interruption processing where when theshort-circuit detection signal is supplied from the short-circuitdetector 82 during the second welding stage (step S81), theshort-circuit current Is(S) and the supply period τs(S) are read outfrom the aforementioned short-circuit current waveform memory 87 and theshort-circuit current whose magnitude increases in step wise iscontinuously supplied by updating the iterative loop till theshort-circuit is removed. After the short-circuit is removed, theprogram returns to the control of the regular welding just before theshort-circuit occurred in FIG. 15 (steps S82-S86).

According to the fourth inventive aspect, the current waveform- ispredivided into the short-circuit current waveform and the arc currentwaveform so that even when short-circuit occurs suddenly due to externaldisturbances during the regular welding, the current waveform isautomatically switched to the short-circuit current waveform. The fourthinventive aspect ensures the improvement of quality of welding inaddition to the effects of the third inventive aspect.

A specific example of the fifth inventive aspect will now be described.The fifth inventive aspect is a pulse welding apparatus of the overallconstruction in FIG. 9 with the separation detector 83 eliminated as inthe fourth inventive aspect. The calculating unit 88 has the algorithmin which when the short-circuit is detected by the short-circuitdetector 82 in the second welding stage, on the basis of the waveformparameters of welding current learned in the first welding stage, theshort-circuit current is read out from the short-circuit currentwaveform memory 87 where both the step-wise short-circuit current Is(S)supplied when short-circuiting and the supplying period τs(S), arestored, and then after the short-circuit is removed, the arc currentwaveform is reset and the arc current waveform is supplied.

That is, the short-circuit current waveform memory 87 holds thestair-case-like short-circuit current Is(S) whose magnitude iscontrolled via the external input/output port 9 to increase the supplyperiod τs(S)(s=1, 2, . . . , So) in steps. The calculating unit 88performs short-circuit interruption processing where when theshort-circuit detection signal is supplied from the short-circuitdetector 82 during the second welding stage (step S91), theshort-circuit current Is(S) and the supply period τs(S) are read outfrom the aforementioned short-circuit current waveform memory 87 and theshort-circuit current whose magnitude increases gradually step wise iscontinuously supplied by updating the iterative loop till theshort-circuit is removed.

After the short-circuit is removed, the arc current waveform is resetand the arc current waveform is supplied for n=0 as shown in FIG. 15(steps S92-S97).

According to the fifth inventive aspect, when the short-circuit occurs,the short-circuit current is immediately run, and after theshort-circuit is removed the arc current waveform is reset beforesupplying the arc current waveform. Thus, in the short-circuit transferarc welding method, the same effects as in the third inventive aspectare obtained.

A specific embodiment of a sixth inventive aspect will now be described.The sixth inventive aspect has the entire construction in FIG. 9. Thecalculating unit 88 has the algorithm where in the regular welding orthe second welding stage, the charge amount of current after the globuleseparates from the electrode is detected in response to the detectionsignal from the separation detector 83, which detects the separation ofglobule grown on the tip of wire electrode, on the basis of the waveformparameters of welding current learned in the first welding in the thirdand fourth inventive aspects so as to run the minimum base current whenthe charge amount is more than a predetermined value.

That is, FIG. 18 shows a flowchart corresponding to steps S39-S41 in theregular welding in FIG. 15. When the separation detection signal isreceived from the separation detector 83 (step S101, S102), the chargeamount Q is reset and then the charge amount after separation of globuleis detected. If the charge amount exceeds a predetermined value Qo, thena minimum base current Is(m,n) is outputted (step S105). Afterseparation, the program immediately jumps from step S101 to step 104. Ifthe answer is "NO" at steps s102 and S104, the program proceeds to steps106-107 where the respective parameters are corrected. After step S107,the charge amount Q is corrected by an equation Q=Q+Ip(m,n)τ(m,n) atstep S108. The rest of the flowchart is the same as that in FIG. 15.

In the sixth inventive aspect, the total charge amount of current over atime length after detection of separation is detected and then thecurrent is reduced when the thus detected charge amount reaches thepredetermined value. Thus, the amount of globule when separating may bemaintained nearly constant allowing welding operation to be in moreregular manner.

In the regular welding, the sixth inventive aspect has the algorithmwhere the charge amount of current after separation is detected on thebasis of the detection signal from the separation detector 83 thatdetects the separation of globule formed on the tip of the wireelectrode, and the minimum base current is run when the charge amountexceeds the predetermined value.

That is, FIG. 18 shows a flowchart corresponding to steps S39-S41 in theregular welding in FIG. 15. When the separation detection signal isissued by the separation detector 83 (step S101, S102), the chargeamount Q is reset and then the charge amount after separation isdetected. If the charge amount exceeds the predetermined value Qo, theminimum base current I_(B) (m,n) is outputted (step S105). Afterseparation, the program jumps to step S104. If the answer is NO at stepS102 or S104, the program proceeds to S106 or S107, respectively, wherethe respective parameters are corrected. At step S108, the charge amountQ is corrected according to the equation Q=Q+Ip(m,n)τ(m,n). The rest offlowchart is the same as that in FIG. 15.

In addition to the effects derived from the third and fourth inventiveaspects, the sixth inventive aspect has the advantage that the chargeamount of current over a time length after separation is detected andthen the current is reduced when the thus detected charge amount reachesthe predetermined value. Thus, the amount of globule during separationmay be maintained nearly constant allowing welding operation in moreregular manner.

A specific embodiment of a seventh inventive aspect will now bedescribed. The seventh inventive aspect is a pulse welding apparatus ofthe construction in FIG. 9 with the short-circuit detector 82, theseparation detector 83, and the short-circuit current waveform memory 87removed. The calculating unit 88 has the algorithm which has a storagemeans which operates to write the target arc length signal into theaforementioned target arc length memory 86 for storage, the target arclength being corrected and learned on the basis of the detected arclength signal when welding is performed by the current waveform on thebasis of the predetermined arc current waveform parameters, and acontrol means which controls the arc current waveform parameters toincrease or decrease in accordance with the difference between theaforementioned detected arc length signal and the learned target arclength signal.

The operation of the seventh inventive aspect will now be described withreference to the flowchart of the calculating unit 88 in FIGS. 19 and20.

FIG. 19 shows the flowchart of the first welding stage as learningwelding. The welding is performed on the basis of the pulse currentwaveform parameters stored in the arc current waveform memory 85 definedvia the external input/output port 9. The target arc length signal Lo(n)is corrected according to the equation Lo(n)=1/2[Lo(n)+L(l)]on the basisof the detected arc length signal L(l) detected during the welding.Then, the target arc length signal Lo(n) is written into the target arclength memory 86. FIG. 20 shows the flowchart of the second weldingstage as the regular welding. In the figure, the learned target arclength signal which has been written into the target arc length memory86 in the aforementioned first welding stage, and the arc waveformparameters are controlled to increase or decrease in accordance with thedifference between the detected arc length signal and the learned targetarc length signal.

In the first welding stage as the learning welding shown in FIG. 19, therespective parameters of pulse current group Ip(n), I_(B) (n), τ(n),C_(A) (n), and target arc length Lo(n) are inputted into the arc currentwaveform memory 85 and the target arc length memory 86 via the externalinput/output port 9.

With this condition, the calculating unit 88 sets the iterative loop ton=1 (step S1, S2), reads the arc current waveform parameters Ip(n),I_(B) (n), τ(1), C_(A) (1), and Lo(1) from the arc current memory 85 andthe target arc length memory 86 (step S3), and outputs the weldingcurrent corresponding to these parameters to the comparator 89 (step S4,S5).

The comparator 89 supplied with the pulse current lo from thecalculating unit 88 in this manner, sends an ON signal to the inverterdrive circuit 2 so that the inverter drive circuit 2 transmits theinverter drive signal to the inverter circuit 1 to drive it. Driving theinverter causes the shaped alternating waveform to be outputted to thehigh frequency transformer 3, which in turn supplies an output to thehigh frequency diodes 4A and 4B by which the signal is converted into aDC waveform. Thereby, the pulse arc current i is supplied to the arcload unit 5. This pulse arc current i produces the pulse arc discharge53 across the wire electrode 52 and the workpieces 54 to melt both theworkpieces 54 and the tip end of wire electrode 52 by the pulse arcdischarge.

The arc length detector 81 detects the arc length L(l) on the basis ofthe detection signal I of the current detector 6 and the detectionsignal V of the voltage detector 7 so as to output the detection signalsto the calculating unit 88. When the supply of arc current has beencompleted for n=1, i.e., when the t=τ(1)+C_(A) (1) is satisfied (stepS6), the calculating unit 88 reads the aforementioned detected arclength L(l) (step S7), and corrects the target arc length signal Lo(n)according to the equation below while also updating the target arclength Lo(n) in the target arc length memory 86 (step S8).

Then the program goes through steps S9-S11 and clears the time to t=0and then returns to step S2 where the iterative loop of the pulse groupis updated to n=2. If n≧2, the arc current waveform parameters and thetarget arc length detection signal are read in at step S3 so as correctthe arc current waveform parameters on the basis of the difference ΔLbetween the arc length detection signal L(l) and the target arc lengthsignal Lo(n) (step S13, S14).

    Ip(n)=Ip(n)-B.sub.1 ΔL

    I.sub.b (n)=I.sub.B (n)-B.sub.2 ΔL

    τ9n)=τ(n)-B.sub.3 ΔL

    C.sub.A (n)=C.sub.A (n)-B.sub.4 ΔL

(B₄ -B₄ are proportional constants)

When the difference ΔL is determined, the previous value of thedifference ΔL for (n-1) is used as the arc length detection signal L(l).Then, the pulse is outputted in accordance with the arc current waveformparameters corrected as mentioned above (step S14, S15). Then, theprogram returns to step S7 where the arc length detection signal L(l) isread in accordance with the pulse output so as to update the target arclength signal stored in the target arc length memory 86 at step S8. Theabove-mentioned signal processing is iterated till n=n_(o) for therespective pulse current groups (step S10-S12).

The target arc length signal stored in the target arc length memory 86in the first welding stage is stored as a learned target arc lengthsignal taking the magnetic blow into account, and serves to eliminatethe effect of the changes of arc length on welding quality due tomagnetic blow and to control the faulty separation of globules.

The welding operation shifts to the regular welding as the secondwelding stage as shown in FIG. 20 after the learning welding as thefirst welding stage. The regular welding shown in FIG. 20 has thesubstantially the same flowchart as the learning welding shown in FIG.19, the program reads out the target arc length Lo(n) learned in thelearned welding and stored in the target arc length memory 86, the stepS8 in FIG. 19 is deleted, and at step S27 similar to step S14 theaforementioned arc current waveform parameters are corrected inaccordance with the difference L between the previous arc lengthdetection signal L(l) and the target arc length signal Lo(n), and thepulses are outputted on the basis of the thus corrected parameters.

    IP(n)=Ip(n)-B.sub.I ΔL

    I.sub.b (n)=I.sub.B (n)-B.sub.2 ΔL

    Δ(n)=Δ9n)-B.sub.3 ΔL

    C.sub.A (n)=C.sub.A (n)-B.sub.4 ΔL

(B₁ -B₄ are proportional constants)

Thus, in the regular welding as the second welding stage, the currentwaveform is controlled so as to produce the same arc length signal asthe target arc length which is learned in the first welding stage. Thisis effective in controlling the faulty separation of globules due toexternal disturbances occurring at the welding torch for improvedwelding quality under various welding environments.

In addition to the effects derived from the first and second inventiveaspect, the embodiment of the seventh inventive aspect is advantageousin that the effect of magnetic blow on the arc length variation iseliminated in the first welding stage, the faulty separation of globulesdue to the magnetic blow is controlled, and the target arc length signallearned taking the magnetic blow into account in the respective weldingregions is obtained, the variations of the arc lengths due to externaldisturbances occurring in the magnetic blow are controlled for improvedwelding quality under various welding environments.

A specific embodiment of an eighth inventive aspect will now bedescribed. The eighth inventive aspect is a pulse welding apparatus ofthe same construction as in FIG. 9 with the separation detector 83removed. The calculating unit 88 has an algorithm in which forperforming the regular welding as the second welding stage in accordancewith the waveform parameters of welding current learned in the firstwelding stage, when the short-circuit is detected by the short-circuitdetector 82, the short-circuit current is read out from the shortcircuit current waveform memory 87 for supplying current, in whichmemory the short-circuit current Is(S) supplied during short-circuitperiod and the time duration τs(S) are stored.

That is, in the short-circuit current waveform 87 are stored thestair-case like short-circuit current Is(S) whose value increasesgradually and the time duration τs(S) (S=1,2, . . . , So) by means ofthe external input/output port 9. Through interruption handling routine,in performing the second welding stage, when the calculating unit 88receives the short-circuit detection signal from the short-circuitdetector 82 (step S81), the unit 88 reads the short-circuit currentIs(S) and the time duration τs(S) of Is(S) from the aforementionedshort-circuit current waveform memory (87) and continues to supply theshort-circuit current whose amplitude is increased in step wise throughthe iterative loop S till the short-circuit is removed. Then, after theshort-circuit is removed, the program returns to the control immediatelybefore the regular welding in FIG. 20 (step S82-S86).

In the eighth inventive aspect, a predetermined current waveform isdivided into the short-circuit current waveform and the arc currentwaveform, and the arc current waveform is switched to the short-circuitcurrent waveform when a sudden short-circuit occurs due to externaldisturbances during the regular welding. Thus, in addition to the effectderived from the seventh inventive aspect, the eighth inventive aspectensures good welding and the quality of products.

An embodiment of a ninth inventive aspect will be described. The ninthinventive aspect is a pulse welding of the construction in FIG. 9without the separation detector 83. The calculating unit 88, during theregular welding as the second welding stage performed in accordance withthe waveform parameters of welding current learned in the first welding,when the short-circuit is detected by the short-circuit detector 82, theshort-circuit current is read out from the short-circuit currentwaveform memory 87 where the short-circuit current Is(S) of stair-casewaveform supplied during the short-circuit and the time duration τs(S)are stored. After short-circuit is removed, the arc current waveform isreset before resuming the supply of arc current waveform.

That is, the time-duration τs(S) (S=1, 2, . . . , So) and theshort-circuit current Is(S) in the form of stair-case where currentincreases in steps, are stored into the short-circuit current waveformmemory 87 through the external input/output port 9. During the secondwelding stage, when the calculating unit 88 receives the short-circuitdetection signal generated through handling operation for short-circuitin FIG. 22 (step S91), the calculating unit 88 reads in theshort-circuit current Is(S) and the time-duration τs(S) from theshort-circuit current waveform memory 87, continues to supply theshort-circuit current whose amplitude increases insteps, by updating theiterative loop S till short-circuit is removed. After the short-circuitis removed, the arc current waveform is reset before supplying arccurrent waveform for n=0 in the regular welding shown in FIG. 20 (stepsS92-S97).

Thus, in the ninth inventive aspect, the short-circuit current is runimmediately when the short-circuit occurs, and after the short-circuitis removed, the arc current is reset before resuming the arc currentwaveform. Thus, the same effects as in the seventh inventive aspect canbe obtained in the short-circuit through arc welding as well.

An embodiment of a tenth inventive aspect will be described. The tenthinventive aspect has the entire construction shown in FIG. 9. During theregular welding as the second welding stage performed in accordance withthe waveform parameters of welding current learned in the first weldingstage of the seventh and eighth inventive aspects, the calculating unit88 receives the detection signal from the separation detector 83 fordetecting the separation of globules produced on the tip of wireelectrode, and detects the charge amount of current after separation sothat the minimum base current is supplied when the charge amount exceedsa predetermined value.

That is, FIG. 23 shows a flowchart corresponding to step 27 of theregular welding shown in FIG. 20. When the calculating unit 88 receivesthe separation signal from the separation detector 83 (step S101, S102),the unit 88 resets the charge amount Q to detect the charge amount afterseparation, and if the predetermined value Qo is exceeded, the minimumbase current I_(B) (n) is outputted (step S105). After undergoingseparation, the program jumps from step S101 to S104. If the answer atstep S102 or S103 is "NO", then the program proceeds to step S106 orS107 where the respective parameters are corrected. Then, at step S108,the charge amount Q is corrected according to Q=Q+Ip(n)×τ(n).

Thus, in addition to those derived from the seventh and eighth inventiveaspects, the tenth inventive aspect has advantages that the chargeamount of current after separation occurs is detected, and the currentis reduced when the detected charge amount reaches a predeterminedvalue. Thus, the amount of globule during separation can be controlledto be substantially constant for performing welding in a regularfashion.

What is claimed is:
 1. A pulse welding apparatus in which pulse currentsfor melting a workpiece are supplied alternately with a base current orwith a short-circuit current to a welding load so as to perform weldingoperation, the apparatus comprising:an arc welding power supply unit forsupplying said pulse currents to the welding load, in which one waveformof said pulse currents is further divided into a group of pulse currentswhich has at least one pulse width and at least one pulse interval,which is obtained to periodically repeat said group of pulse currentsand to superpose with a continuous base current; a voltage detectingcircuit for detecting the output of said arc welding power supply unit;a smoothing circuit for receiving the output signal of said voltagedetecting circuit; a voltage setting circuit for setting a desiredoutput voltage; and a microcomputerized digital circuit including adigital/analog converter circuit for outputting a voltage signalcorresponding to a desired output current to said arc welding powersupply unit, a first analog/digital converter circuit for receiving theoutput signal of said voltage setting circuit, a second analog/digitalconverter circuit for receiving the output signal of said smoothingcircuit, a data latch circuit having multiple bits output signal linesconnected with multiple bits input signal lines of the digital/analogconverter circuit, a CPU connected, via a common data bus, to each ofsaid multiple bits input signal lines of the data latch circuit, saidmultiple bits output signal lines of the first analog digital convertercircuit, and said multiple bits output signal lines of the second analogdigital converter circuit; wherein said CPU operates, when said arcwelding power supply unit outputs the base current or the short-circuitcurrent, such that a digital data V_(FBA) corresponding to an averageoutput voltage of the arc welding power supply unit is compared with adigital data Vset corresponding to a desired output voltage atpredetermined time intervals so as to maintain the base current or theshort-circuit current or to output a melting current for the workpiecesinstead of the base current or the short-circuit current.
 2. A pulsewelding apparatus according to claim 1, wherein said CPU is a singlechip CPU which incorporates said first and second analog/digitalconverting circuits.
 3. A pulse welding apparatus according to claim 1,wherein said CPU is a single chip CPU which incorporates a ROM.
 4. Apulse welding apparatus according to claim 1, wherein said CPU is asingle chip CPU which incorporates said first and second analog/digitalconverting circuits and said ROM.
 5. A pulse welding apparatus accordingto any one of claims 1, 2, 3, or 4, wherein said apparatus furtherincludes:a third analog/digital converter circuit receiving the outputof the voltage detecting circuit and having a multiple bits signal linesconnected to the data bus, and said CPU, when the arc welding powersupply unit outputs the base current or short-circuit current,performing operations according to an algorithm at predeterminedintervals, having another algorithm in which a digital data V_(FBM)corresponding to a momentary output voltage of the arc welding powerunit is compared with a digital data Vmax in which the character isVmax > Vset corresponding to the predetermined digital data Vset, so asto maintain the base current or the short-circuit current when V_(FBM) >Vmax and output a second base current or a second short-circuit currentgreater than the base current or the short-circuit current only whenV_(FBM) ≧ Vmax.
 6. A pulse welding apparatus according to claim 5,wherein said CPU is a single chip CPU having the third analog digitalconverting circuit incorporated.